Document and Entity Information
| Document and Entity Information | Jun. 28, 2021 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Jun. 28, 2021 |
| Entity Registrant Name | ARCA biopharma, Inc. |
| Entity Central Index Key | 0000907654 |
| Entity File Number | 000-22873 |
| Entity Incorporation, State or Country Code | DE |
| Entity Tax Identification Number | 36-3855489 |
| Entity Address, Address Line One | 10170 Church Ranch Way |
| Entity Address, Address Line Two | Suite 100 |
| Entity Address, City or Town | Westminster |
| Entity Address, State or Province | CO |
| Entity Address, Postal Zip Code | 80021 |
| City Area Code | 720 |
| Local Phone Number | 940-2200 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common |
| Trading Symbol | ABIO |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | false |
| Current Fiscal Year End Date | --12-31 |